Lasers based on excitation by photodissociation were first reported in 1964 and employed lasing in iodine by dissociating an alkyl iodide. Later reports involved excitation in the infrared region of the spectrum involving bromine or an alkali metal. More recently laser action has been generated by photodissociation of mercuric bromide (HgBr.sub.2) in the vapor phase when pumping with an ArF excimer laser, generating 193 nm wavelength output. The produced laser action exhibited a wavelength of 502 nm. As discussed by Schimitschek and co-workers, in U.S. Pat. Nos., 4,168,475; 4,228,408; and 4,229,711, the overall efficiency of such systems is very low, being generally about 1-3%.
The aforementioned patents generally relate to pumping dissociated mercuric halides. These molecules lase in interesting spectral regions by recombination of radicals with emission of radiation energy (HgCl:yellow-green at 557 nm; HgBr:blue-green at 502 nm; and HgI:violet at 440 nm) but their development has been very slow. Most of the work to date has involved the radical HgBr because of government interest in possible use for undersea communication systems.
If one wishes to pump such lasers optically, it has been necessary to use an optical source that emits photons having a wavelength of about 200 nm. This has generally meant the use of an ArF laser (193 nm) but the overall efficiency is limited to that of the ArF laser. Such laser photons are very expensive and, accordingly, such pumping means are not commercially attractive. Electrically pumped lasers of this type have been limited to short pulse lengths, typically less than 1 microsecond. It is very difficult to sustain a uniform "glow" discharge for more than several hundred nanoseconds. In such systems the HgX.sub.2 (X=I, Br or Cl) molecule must reform in each cycle and this is a slow process. Furthermore, depletion of the HgX.sub.2 "fuel" also limits laser pulse lengths. These features as well have limited commercial development.
An improved mercury bromide laser, lasing in the visible blue-green spectrum would be of great interest in essentially revolutionizing military satellite-to-submarine communication. Improved metal halide lasers generally would be of interest for other purposes, such as medical applications, as well. Thus, there is an intriguing need for the development of such lasers having commercially attractive energy efficiencies in both pulsed and continuous-wave systems.